The present invention relates to a fuel reforming apparatus especially adapted for use with an internal combustion engine, the apparatus including a burning chamber and a catalytic reactor for converting the hydrocarbon fuel into a reformed gas which may be easily burned in the internal combustion engine, whereby the ignitibility and combustibility of the fuel as well as the fuel consumption may be considerably improved and toxic gas emission may be minimized.
In order to minimize toxic gas emission, in both conventional internal combustion engines and stratified combustion engines, it has been required to atomize and evenly distribute the fuel into the cylinders of the engine. For this purpose, there have been devised and demonstrated various fuel supply systems for heating and vaporizing use of fuel by the hot cooling water or exhaust gases, but they have a common defect that the efficient and effective vaporization of the fuel cannot be attained under all the operating conditions of the engine.
High-octane fuel for internal combustion engines contains aromatic hydrocarbons and lead compounds so that toxic gases are produced and emitted, presenting serious atmospheric pollution problems.
The present invention was made to overcome the above and other problems, and a first feature of the present invention resides in the fact that a fuel reforming apparatus includes a burning chamber wherein a part of a hydrocarbon fuel to be charged into the engine is burned in a suitable air-fuel ratio, and a catalytic reactor which is packed with a suitable catalyst adapted to carry out catalytic reformation with the aid of the heat of the combustion gases from the burning chamber, of the hydrocarbon fuel under the condition that almost no oxygen is present in the reactor, thereby producing a reformed gas rich with hydrogen which may be further mixed with the raw hydrocarbon fuel to be charged into the engine. Therefore, a first object of the present invention is to make the engine operate with a relatively lean air-fuel mixture, thereby minimizing toxic gas emission.
A second feature of the present invention resides in the fact that both the combustion gases discharged from the burning chamber and the hydrocarbon fuel are reformed within the catalytic reactor. Therefore, in addition to the first object described above, the present invention has a second object to suppress the production of carbon to a minimum in the catalytic reforming process in the catalytic reactor.
A third feature of the present invention resides in the fact that the hydrocarbon fuel and water supplied through an independent water supply system are charged into the catalytic reactor to be converted into a reformed gas. Therefore, the present invention has a third object, in addition to the first object, to positively suppress the production of carbon in the catalytic reforming process in the catalytic reactor.
In existing chemical plants, partial oxidation, steam reforming and thermal cracking methods have been used together with catalysts to convert hydrocarbons into reformed gas, and the fuel reforming apparatus in such plants are stationary and are operated under steady state conditions so that the control of the quantity of hydrocarbon fuel supply and the control of the reaction temperature can be attained in a simple manner. Furthermore, the heat source may be controlled easily and the reaction conditions may be adjusted in a simple manner. Moreover, the installation space of the apparatus is not critical. However, in the case of the fuel reforming apparatus for use with internal combustion engines, the operating conditions change from time to time, and so do the reaction conditions. Furthermore, it is extremely difficult to provide sufficient heat when the engine is started. According to the present invention, however, a part of the hydrocarbon fuel is burned so that when the engine is started, the fuel reforming apparatus may be immediately raised to a high temperature sufficient to continuously carry out catalytic reformation. Moreover, the fuel reforming apparatus in accordance with the present invention is compact in size and light in weight, and the reaction temperature may be controlled in a simple manner.
According to the present invention, a part of a hydrocarbon fuel is mixed with air to provide a combustion mixture in a suitably combustible air-fuel ratio so that the combustion mixture may be ignited and burned within a burning chamber without producing any soot or carbon. Soot or carbon will poison the catalyst in a reactor so that the air-fuel ratio of the combustion mixture must be selected depending upon the construction of the burning chamber, the vaporization of the hydrocarbon fuel, and so on. The heat of the combustion gases is used to heat the catalytic reactor so that the catalyst in it may be maintained at a suitable temperature. Furthermore, the combustion gases are charged into the reactor so that the hydrocarbon fuel may be converted into a reformed gas within the reactor without the presence of excessive oxygen or air. Alternatively, the combustion gases from the burning chamber may be discharged into the air intake system or the exhaust manifold of the engine. The quantity of the combustion mixture to be charged into the burning chamber is so selected that the heat enough to heat the catalytic reactor to a desired reaction temperature may be generated.
The hydrocarbon fuel charged into the catalytic reactor is made to contact with the catalyst packed within the catalytic reactor to be converted into a reformed gas rich with hydrogen with the aid of the heat of the combustion gases. Alternatively, a mixture of the hydrocarbon fuel and burning gases from the combustion chamber is charged into the reactor to be converted into a reformed gas. In the latter case, care should be taken so that the hydrocarbon fuel may not be exposed directly to the combustion flames. In other words, the hydrocarbon to be reformed must not be charged together with the combustion mixture into the burning chamber. Otherwise, soot is produced and is attached to the catalyst in the reactor, thereby adversely affecting the service life of the catalyst. The short service life of the catalyst presents a very serious problem especially in the case of the fuel reforming apparatus mounted on a vehicle for the purpose of reducing toxic gas emission from the engine. When a rich mixture of hydrocarbon fuel and air is charged into the burning chamber in order to burn only a fraction of it, there will be produced layers of combustion gases and the rich mixture in the burning chamber. As a result, in one layer, the supply of oxygen will be insufficient while in the other layer, the supply of oxygen will be excessive so that large amounts of soot or carbon may be produced. In order to overcome these problems, according to the present invention, hydrocarbon fuel is mixed with the combustion gases from the burning chamber downstream thereof so that the hydrocarbon fuel may be prevented from being directly exposed to the combustion flames and may be uniformly mixed with the combustion gases before it is charged into the catalytic reactor.
According to the present invention, the fuel reforming process carried in the catalytic reactor causes essentially an endothermic reaction with little air or with little oxygen being introduced into the catalytic reactor so that thermal runaway may be prevented. Therefore, it is essential that a combustion mixture with a suitable air-fuel ratio must be ignited and burned in the burning chamber, and that hydrocarbon fuel must be charged into the catalytic reactor in such a way that little oxygen or air may be introduced into the catalytic reactor. It is preferable that the temperature of the endothermic reaction be maintained in a range between 500.degree. and 800.degree. C. In order to stabilize the reaction within the catalytic reactor, to relax the reaction conditions and to improve the conversion efficiency, it is preferable to use a catalyst such as nickel, cobalt, chromium, platinum, rhodium or the mixture thereof. Whatever the type of the catalyst used, it is essential that the catalyst should convert the hydrocarbon fuel into a reformed gas rich with hydrogen.
As described above, according to the present invention, a reformed gas rich with hydrogen may be obtained, and the combustion of hydrogen is about 8 times as fast as that of conventional gasoline fuel so that the combustion efficiency in the internal combustion engines may be much improved. More particularly, a lean combustion mixture, which has been hitherto impossible to ignite and burn in an internal combustion engine with a carburetor, can be positively ignited and burned so that toxic gas emission may be minimized and fuel consumption may be considerably improved. As compared with the fuel which is atomized and vaporized by conventional carburetors, the reformed gas may be more evenly distributed among the cylinders of an engine because the reformed gas is completely in the form of a gas. Therefore, toxic gas emission may be further minimized. Although conventional high-octane fuel contains aromatic hydrocarbons and lead compounds which are harmful to persons, the reformed gas does not require any aromatic hydrocarbon and lead compounds, because the reformed gas itself changes into high-octane fuel. Therefore, any hydro-carbon such as naphtha may be advantageously used. This means that the fuel may be selected from a wide range of various hydrocarbons.